When the umpire turns and makes the international sign for referral, all play stops and time seems suspended. On the pitch and on the bench more than 40 pairs of eyes pivot towards the big screen and, across the world, hockey aficionados begin to speculate on what decision will be made.
For the video umpire, shut away in a room full of screens, this is the moment when they spring into action. But as Belgium umpire Celine Martin-Schmets explains, it is also a moment when you feel as if you are in a bubble, shut away from all the emotion and tension that is out on the field of play.
"It is only after the decision has been made do you feel the adrenaline and the nerves kick in," she says.
The video referral has been around for nearly a decade in hockey and in that time it has become a trusted and vital tool for both the umpires and the teams.
For the players and coaching staff it offers a chance to question an often crucial decision and learning how to effectively and correctly use the referral is as much a skill as any other element of the game.
For the umpires, it is an opportunity to avoid making an error or to reinforce a decision.
England's Emma Shelbourn explains how the work of the umpiring team, including the video umpire, starts from well before the opening match of a competition: "Initially, when we arrive at a tournament we will meet with the video umpire coach and the umpire managers and we will have a briefing. We will watch some video clips and make decisions on those clips and we will talk about consensus and make sure we are on the same page before the tournament starts.
"Prior to the tournament starting, we have a lot of clips, which we share on a dedicated Facebook page. As a group we are constantly discussing and reviewing decisions. It is important before you arrive to know where the standards are set and what we are going to award and what we will not award."
Foresight is a valuable asset in the world of the video umpire. "Being constantly on your toes is important," says Martin-Schmets, "having an awareness of what might happen next or come up during the game helps you prepare for any eventuality."
The video umpire is not alone in the video box. He or she has a constant line of communication to both the on-pitch officials and the Hawkeye team who provide the various angles of playback.
It is also useful to have prior knowledge of the teams and the coaches and the way they approach referrals. Some teams make the decisions on the pitch, others rely on coaches' calls from the sideline. Knowing what is likely to spark a referral or when in the game it might occur is all helpful knowledge.
For this reason, the umpires will spend a lot of time reviewing previous competitions. The 'eye in the sky' always has eyes on the match, says Shelbourn. "When you do get a referral, you need to understand the context in which the umpire's decision has been made. For example, the umpire may have played an advantage. You need to know that as it can affect the final decision. A defending team may be calling for a foot in the circle but there had already been an earlier infringement of which the umpire was aware and she was just holding her whistle – we must know the full context of the game."
Once a referral is called, both Martin–Schmets and Shelbourn agree that the first view must be in real time. That gives the video umpire an initial feel as to what the decision should be. This will be followed by viewing a number of different angles and may call for slow-motion (slow-mo) replay. When a decision is reached, it is clearly communicated back to the umpire.
Language is an important consideration. Both umpires and players are expected to carry out a referral in English, so for those for who English is a second language, time and support is necessary. Martin-Schmets said one marked development in recent years has been the amount of time and practice both China and Japan have paid to getting the communications around video referral correct.
Experience as a video umpire does impact the way that people then return to umpiring roles. "It doesn't change the way you umpire but you are more aware that someone has your back," says Martin–Schmets. "You blow what you see but if you don't see everything, then the video umpire is there to support."
"It has made us much more accountable in our circles," says Shelbourn. "We work very hard on our positioning and getting to the baseline to get that great angle. It also adds clarity to a situation. We might see something that is strange – not necessarily an infringement but not quite right. We can clock it and go back to check it once play breaks.
"Also, if you are watching the ball, your colleague is watching the players. And we can go to a video at any point. The level of accountability is so much higher and that is brilliant for the game."
Video umpires can call up many different angles, and different cameras will provide different perspectives. A view from the centre of the goal might be used when a defender and attacker are running together for a ball; a flat, side-line camera will pick up whether the ball has gone out of the circle on a penalty corner.
As Shelbourn points out however, you can get too much information. "If there is something we need to look at from 10-15 angles, then it is probably not there. You need to stay objective. Use slow motion when you need to, not just because it is available. And you have to accept that sometimes there are situation where there is just no advice because of the angles or where the players are stood in front of the ball."
And then of course, there is that moment when the playback on the big screen is not the same as the playback the video umpire is seeing. "Yes, that is difficult," agrees Shelbourn. "But this is when it is so important that the on-pitch umpire totally trusts the person in the box. The crowd can be shouting, the players gesticulating, but the person who is seeing every angle is your colleague in the video box."
For the umpires at the Wanglibao Hockey Champions Trophy in Changzhou, a source of support and guidance has been the video umpire manager, Carol Metchette of Ireland.
An umpire with years' of experience, Metchette has been training a new generation of video umpires. "Carol gives us a wealth of experience," says Martin–Schmets. "When you start out she really opens your eyes to what you should look for. For example, in my second referral, a danger/no danger situation. We looked at all the angles but she said, 'before you look at any of that, look at the reaction of the player, that will tell you a lot'. I was looking for the ball but the reaction of the player in that instance was the telling point.
"She talks about taking all the pieces together to solve the puzzle. That is a very good way of looking at it."
The message that comes out loud and clear from the interview is the teamwork and trust that has to exist between the umpires on the pitch and their guardian 'eyes in the sky'.
"When you go into changing room, you talk it through and agree how you will approach the match," says Shelbourn. "When you part ways to be the 'eyes in the sky', your fellow umpires have to know you have their back and any decision is evidence-based and nothing is subjective."